Metal telluride nanosheets by scalable solid lithiation and exfoliation.

Transition metal tellurides (TMTs) have been ideal materials for exploring exotic properties in condensed-matter physics, chemistry and materials science1-3. Although TMT nanosheets have been produced by top-down exfoliation, their scale is below the gram level and requires a long processing time, restricting their effective application from laboratory to market4-8. We report the fast and scalable synthesis of a wide variety of MTe2 (M = Nb, Mo, W, Ta, Ti) nanosheets by the solid lithiation of bulk MTe2 within 10 min and their subsequent hydrolysis within seconds. Using NbTe2 as a representative, we produced more than a hundred grams (108 g) of NbTe2 nanosheets with 3.2 nm mean thickness, 6.2 µm mean lateral size and a high yield (>80%). Several interesting quantum phenomena, such as quantum oscillations and giant magnetoresistance, were observed that are generally restricted to highly crystalline MTe2 nanosheets. The TMT nanosheets also perform well as electrocatalysts for lithium-oxygen batteries and electrodes for microsupercapacitors (MSCs). Moreover, this synthesis method is efficient for preparing alloyed telluride, selenide and sulfide nanosheets. Our work opens new opportunities for the universal and scalable synthesis of TMT nanosheets for exploring new quantum phenomena, potential applications and commercialization.

Carrier Transport Regulation of Pixel Graphene Transparent Electrodes for Active-Matrix Organic Light-Emitting Diode Display.

Integrating a graphene transparent electrode (TE) matrix with driving circuits is essential for the practical use of graphene in optoelectronics such as active-matrix organic light-emitting diode (OLED) display, however it is disabled by the transport of carriers between graphene pixels after deposition of a semiconductor functional layer caused by the atomic thickness of graphene. Here, the carrier transport regulation of a graphene TE matrix by using an insulating polyethyleneimine (PEIE) layer is reported. The PEIE forms an ultrathin uniform film (≤10 nm) to fill the gap of the graphene matrix, blocking horizontal electron transport between graphene pixels. Meanwhile, it can reduce the work function of graphene, improving the vertical electron injection through electron tunneling. This enables the fabrication of inverted OLED pixels with record high current and power efficiencies of 90.7 cd A-1 and 89.1 lm W-1 , respectively. By integrating these inverted OLED pixels with a carbon nanotube-based thin-film transistor (CNT-TFT)-driven circuit, an inch-size flexible active-matrix OLED display is demonstrated, in which all OLED pixels are independently controlled by CNT-TFTs. This research paves a way for the application of graphene-like atomically thin TE pixels in flexible optoelectronics such as displays, smart wearables, and free-form surface lighting.

Uniform self-rectifying resistive random-access memory based on an MXene-TiO2 Schottky junction.

For filamentary resistive random-access memory (RRAM) devices, the switching behavior between different resistance states usually occurs abruptly, while the random formation of conductive filaments usually results in large fluctuations in resistance states, leading to poor uniformity. Schottky barrier modulation enables resistive switching through charge trapping/de-trapping at the top-electrode/oxide interface, which is effective for improving the uniformity of RRAM devices. Here, we report a uniform RRAM device based on a MXene-TiO2 Schottky junction. The defect traps within the MXene formed during its fabricating process can trap and release the charges at the MXene-TiO2 interface to modulate the Schottky barrier for the resistive switching behavior. Our devices exhibit excellent current on-off ratio uniformity, device-to-device reproducibility, long-term retention, and endurance reliability. Due to the different carrier-blocking abilities of the MXene-TiO2 and TiO2-Si interface barriers, a self-rectifying behavior can be obtained with a rectifying ratio of 103, which offers great potential for large-scale RRAM applications based on MXene materials.

A polymer electrolyte design enables ultralow-work-function electrode for high-performance optoelectronics.

Ambient solution-processed conductive materials with a sufficient low work function are essential to facilitate electron injection in electronic and optoelectronic devices but are challenging. Here, we design an electrically conducting and ambient-stable polymer electrolyte with an ultralow work function down to 2.2 eV, which arises from heavy n-doping of dissolved salts to polymer matrix. Such materials can be solution processed into uniform and smooth films on various conductors including graphene, conductive metal oxides, conducting polymers and metals to substantially improve their electron injection, enabling high-performance blue light-emitting diodes and transparent light-emitting diodes. This work provides a universal strategy to design a wide range of stable charge injection materials with tunable work function. As an example, we also synthesize a high-work-function polymer electrolyte material for high-performance solar cells.

A photon-controlled diode with a new signal-processing behavior.

The photodetector is a key component in optoelectronic integrated circuits. Although there are various device structures and mechanisms, the output current changes either from rectified to fully-on or from fully-off to fully-on after illumination. A device that changes the output current from fully-off to rectified should be possible. We report the first photon-controlled diode based on a n/n- molybdenum disulfide junction. Schottky junctions formed at the cathode and anode either prevent or allow the device to be rectifying, so that the output current of the device changes from fully-off to rectified. By increasing the thickness of the photogating layer, the behavior of the device changes from a photodetector to a multifunctional photomemory with the highest non-volatile responsivity of 4.8 × 107 A/W and the longest retention time of 6.5 × 106 s reported so far. Furthermore, a 3 × 3 photomemory array without selectors shows no crosstalk between adjacent devices and has optical signal-processing functions including wavelength and power-density selectivity.

Key factors for ultra-high on/off ratio thin-film transistors using as-grown carbon nanotube networks.

Approximately 30% of as-grown carbon nanotube (CNT) networks are metallic, usually leading to a trade-off between carrier mobility and on/off ratio in CNT thin-film transistors (TFTs). Figuring out the key factors of ultra-high on/off ratio in CNT TFTs should be considerably essential for the development of large-scale electronic devices in the future. Here ultra-high on/off ratios of 107-108 are realized for CNT TFTs with mobility of ∼500 cm2 V-1 s-1. We propose that one of the key factors to achieve the high on/off ratio is a clean CNT thin film without charge traps and doping due to residual dispersant used in conventional solution processes. Moreover, on/off ratio degradation under operation voltage is significantly suppressed by decreasing the diameter of CNTs.

Engineering Graphene Grain Boundaries for Plasmonic Multi-Excitation and Hotspots.

Surface plasmons, merging photonics and electronics in nanoscale dimensions, have been the cornerstones in integrated informatics, precision detection, high-resolution imaging, and energy conversion. Arising from the exceptional Fermi-Dirac tunability, ultrafast carrier mobility, and high-field confinement, graphene offers excellent advantages for plasmon technologies and enables a variety of state-of-the-art optoelectronic applications ranging from tight-field-enhanced light sources, modulators, and photodetectors to biochemical sensors. However, it is challenging to co-excite multiple graphene plasmons on one single graphene sheet with high density, a key step toward plasmonic wavelength-division multiplexing and next-generation dynamical optoelectronics. Here, we report the heteroepitaxial growth of a polycrystalline graphene monolayer with patterned gradient grain boundary density, which is synthesized by creating diverse nanosized local growth environments on a centimeter-scale substrate with a polycrystalline graphene ring seed in chemical vapor deposition. Such geometry enables plasmonic co-excitation with varied wavelength diversification in the nanoscale. Via using high-resolution scanning near-field optical microscopy, we demonstrate rich plasmon standing waves, even bright plasmonic hotspots with a size up to 3 µm. Moreover, by changing the grain boundary density and annealing, we find the local plasmonic wavelengths are widely tunable, from 70 to 300 nm. Theoretical modeling supports that such plasmonic versatility is due to the grain boundary-induced plasmon-phonon interactions through random phase approximation. The seed-induced heteroepitaxial growth provides a promising way for the grain boundary engineering of two-dimensional materials, and the controllable grain boundary-based plasmon co-generation and manipulation in one single graphene monolayer will facilitate the applications of graphene for plasmonics and nanophotonics.

Fermi-Level Depinning in Metal/Ge Junctions by Inserting a Carbon Nanotube Layer.

Germanium (Ge)-based devices are recognized as one of the most promising next-generation technologies for extending Moore's law. However, one of the critical issues is Fermi-level pinning (FLP) at the metal/n-Ge interface, and the resulting large contact resistance seriously degrades their performance. The insertion of a thin layer is one main technique for FLP modulation; however, the contact resistance is still limited by the remaining barrier height and the resistance induced by the insertion layer. In addition, the proposed depinning mechanisms are also controversial. Here, the authors report a wafer-scale carbon nanotube (CNT) insertion method to alleviate FLP. The inserted conductive film reduces the effective Schottky barrier height without inducing a large resistance, leading to ohmic contact and the smallest contact resistance between a metal and a lightly doped n-Ge. These devices also indicate that the metal-induced gap states mechanism is responsible for the pinning. Based on the proposed technology, a wafer-scale planar diode array is fabricated at room temperature without using the traditional ion-implantation and annealing technology, achieving an on-to-off current ratio of 4.59 × 104 . This work provides a new way of FLP modulation that helps to improve device performance with new materials.

Laminated three-dimensional carbon nanotube integrated circuits.

The fabrication procedure for each layer of the device in monolithic three-dimensional (3D) integration still follows the design philosophy of traditional planar silicon-based circuits, and such integrated circuits will ultimately be limited by the same scaling constraints that face silicon field-effect transistors. We report the direct formation of laminated 3D integrated circuits by the layer-by-layer stacking of each component through two different techniques. One is to use carbon nanotubes (CNTs) as the channels of thin-film transistors because of their low-temperature fabrication and layer-to-layer transfer capabilities. The other is to use a suitable separator between every two layers to isolate them, because the separator is not only able to maintain the stability of the performance of each component after coating, but is also a good insulator that can prevent interlayer interactions. A 5-stage CNT ring oscillator laminated onto a single inverter is finally reported, which can reduce the device area by approximately 80%, and should be greatly helpful for the continuous improvement of device functionality and integration.

Umbilical Cord Blood Mononuclear Cell Treatment for Neonatal Rats With Hypoxic Ischemia.

Background: Hypoxic-ischemic encephalopathy (HIE) occurs when an infant's brain has not received adequate oxygen and blood supply, resulting in ischemic and hypoxic damage. Currently, supportive care and hypothermia therapy have been the standard treatment for HIE. However, there are still over 20% of treated infants died and 19-30% survived with significant disability. HIE animal model was first established by Rice et al., involving the ligation of one common carotid artery followed by hypoxia. In this study, we investigated human umbilical cord blood (HUCB) and its two components mononuclear cell (MNC) and red cell fraction (RCF) in both short and long term study using a modified HIE rat model. Methods: In this modified HIE model, both common carotid arteries were occluded, breathing 8% oxygen in a hypoxic chamber for 60-min, followed by the release of the common carotid arteries ligature, mimicking reperfusion injury. For cell therapeutic study, cells were intravenously injected to HIE rat pups, and both behavioral and histological changes were assessed at selected time points. Result: Statistically significant behavioral improvements were demonstrated on Day 7 and 1 month between saline treated HIE rats and UCB/MNC treated rats. However, at 3 months, the therapeutic improvements were only showed between saline treated HIE animals and MNC treated HIE rats. For histological analysis 1 month after cell injection, the number of functional neurons were statistically increased between saline treated HIE and UCB/MNC/RCF treated HIE rats. At 3 months, the significant increase in functional neurons was only present in MNC treated HIE rats. Conclusion: We have used a bilateral temporary occlusion of 60 min, a moderately brain damaged model, for cell therapeutic studies. HUCB mononuclear cell (MNC) therapy showed benefits in neonatal HIE rats in both short and long term behavioral and histological assessments.

Patterning of Wafer-Scale MXene Films for High-Performance Image Sensor Arrays.

As a rapidly growing family of 2D transition metal carbides and nitrides, MXenes are recognized as promising materials for the development of future electronics and optoelectronics. So far, the reported patterning methods for MXene films lack efficiency, resolution, and compatibility, resulting in limited device integration and performance. Here, a high-performance MXene image sensor array fabricated by a wafer-scale combination patterning method of an MXene film is reported. This method combines MXene centrifugation, spin-coating, photolithography, and dry-etching and is highly compatible with mainstream semiconductor processing, with a resolution up to 2 µm, which is at least 100 times higher than other large-area patterning methods reported previously. As a result, a high-density integrated array of 1024-pixel Ti3 C2 Tx /Si photodetectors with a detectivity of 7.73 × 1014 Jones and a light-dark current ratio (Ilight /Idark ) of 6.22 × 106 , which is the ultrahigh value among all reported MXene-based photodetectors, is fabricated. This patterning technique paves a way for large-scale high-performance MXetronics compatible with mainstream semiconductor processes.

An ultrasensitive molybdenum-based double-heterojunction phototransistor.

Two-dimensional (2D) materials are promising for next-generation photo detection because of their exceptional properties such as a strong interaction with light, electronic and optical properties that depend on the number of layers, and the ability to form hybrid structures. However, the intrinsic detection ability of 2D material-based photodetectors is low due to their atomic thickness. Photogating is widely used to improve the responsivity of devices, which usually generates large noise current, resulting in limited detectivity. Here, we report a molybdenum-based phototransistor with MoS2 channel and α-MoO3-x contact electrodes. The device works in a photo-induced barrier-lowering (PIBL) mechanism and its double heterojunctions between the channel and the electrodes can provide positive feedback to each other. As a result, a detectivity of 9.8 × 1016 cm Hz1/2 W-1 has been achieved. The proposed double heterojunction PIBL mechanism adds to the techniques available for the fabrication of 2D material-based phototransistors with an ultrahigh photosensitivity.

A flexible ultrasensitive optoelectronic sensor array for neuromorphic vision systems.

The challenges of developing neuromorphic vision systems inspired by the human eye come not only from how to recreate the flexibility, sophistication, and adaptability of animal systems, but also how to do so with computational efficiency and elegance. Similar to biological systems, these neuromorphic circuits integrate functions of image sensing, memory and processing into the device, and process continuous analog brightness signal in real-time. High-integration, flexibility and ultra-sensitivity are essential for practical artificial vision systems that attempt to emulate biological processing. Here, we present a flexible optoelectronic sensor array of 1024 pixels using a combination of carbon nanotubes and perovskite quantum dots as active materials for an efficient neuromorphic vision system. The device has an extraordinary sensitivity to light with a responsivity of 5.1 × 107 A/W and a specific detectivity of 2 × 1016 Jones, and demonstrates neuromorphic reinforcement learning by training the sensor array with a weak light pulse of 1 µW/cm2.

High-performance flexible resistive random access memory devices based on graphene oxidized with a perpendicular oxidation gradient.

The conventional strategy of fabricating resistive random access memory (RRAM) based on graphene oxide is limited to a resistive layer with homogeneous oxidation, and the switching behavior relies on its redox reaction with an active metal electrode, so the obtained RRAMs are typically plagued by inferior performance and reliability. Here, we report a strategy to develop high-performance flexible RRAMs by using graphene oxidized with a perpendicular oxidation gradient as the resistive layer. In contrast to a homogeneous oxide, this graphene together with its distinctive inter-layer oxygen diffusion path enables excellent oxygen ion/vacancy diffusion. Without an interfacial redox reaction, oxygen ions can diffuse to form conductive filaments with two inert metal electrodes by applying a bias voltage. Compared with state-of-the-art graphene oxide RRAMs, these graphene RRAMs have shown superior performance including a high on-off current ratio of ∼105, long-term retention of ∼106 s, reproducibility over 104 cycles and long-term flexibility at a bending strain of 0.6%, indicating that the material has great potential in wearable smart data-storage devices.

A new Hypoxic Ischemic Encephalopathy model in neonatal rats.

BACKGROUND: Hypoxic-Ischemic Encephalopathy (HIE) occurs when an infant's brain does not receive adequate blood and oxygen supply, resulting in ischemic and hypoxic brain damage during delivery. Currently, supportive care and hypothermia have been the standard treatment for HIE. However, there are still a 20% mortality and most of the survivors are associated with significant neurodevelopmental disability. HIE animal model was first established by Vannucci et al., in 1981, and has been used extensively to explore the mechanisms of brain damage and its potential treatment. The Vannucci model involves the unilateral common carotid artery occlusion followed by 90 min hypoxia (8% oxygen). The purpose of this study is to define and validate a modified HIE model which mimics closely that of the human neonatal HIE. METHOD: The classic Vannucci HIE model occludes one common carotid artery followed by 90 min hypoxia. In the new model, common carotid arteries were occluded bilaterally followed by breathing 8% oxygen in a hypoxic chamber for 90, 60 and 30 min, followed by the release of the common carotid artery ligatures, mimicking a reperfusion. RESULT: We studied 110 neonatal rats in detail, following the modified in comparison with the classical Vannucci models. The classical Vannucci model has a consistent surgical mortality of 18% and the new modified models have a 20%-46%. While mortality depended on the duration of hypoxia, fifty-two animals survived for behavioral assessments and standard histology. The modified HIE model with 60 min of transient carotid occlusion is associated with a moderate brain damage, and has a 30% surgical mortality. This modified experimental model is regarded closer to the human situation than the classical Vannucci model.

Pushing the conductance and transparency limit of monolayer graphene electrodes for flexible organic light-emitting diodes.

Graphene has emerged as an attractive candidate for flexible transparent electrode (FTE) for a new generation of flexible optoelectronics. Despite tremendous potential and broad earlier interest, the promise of graphene FTE has been plagued by the intrinsic trade-off between electrical conductance and transparency with a figure of merit (σDC/σOp) considerably lower than that of the state-of-the-art ITO electrodes (σDC/σOp <123 for graphene vs. ∼240 for ITO). Here we report a synergistic electrical/optical modulation strategy to simultaneously boost the conductance and transparency. We show that a tetrakis(pentafluorophenyl)boric acid (HTB) coating can function as highly effective hole doping layer to increase the conductance of monolayer graphene by sevenfold and at the same time as an anti-reflective layer to boost the visible transmittance to 98.8%. Such simultaneous improvement in conductance and transparency breaks previous limit in graphene FTEs and yields an unprecedented figure of merit (σDC/σOp ∼323) that rivals the best commercial ITO electrode. Using the tailored monolayer graphene as the flexible anode, we further demonstrate high-performance green organic light-emitting diodes (OLEDs) with the maximum current, power and external quantum efficiencies (111.4 cd A-1, 124.9 lm W-1 and 29.7%) outperforming all comparable flexible OLEDs and surpassing that with standard rigid ITO by 43%. This study defines a straightforward pathway to tailor optoelectronic properties of monolayer graphene and to fully capture their potential as a generational FTE for flexible optoelectronics.

Chemical vapor deposition of layered two-dimensional MoSi2N4 materials.

Identifying two-dimensional layered materials in the monolayer limit has led to discoveries of numerous new phenomena and unusual properties. We introduced elemental silicon during chemical vapor deposition growth of nonlayered molybdenum nitride to passivate its surface, which enabled the growth of centimeter-scale monolayer films of MoSi2N4 This monolayer was built up by septuple atomic layers of N-Si-N-Mo-N-Si-N, which can be viewed as a MoN2 layer sandwiched between two Si-N bilayers. This material exhibited semiconducting behavior (bandgap ~1.94 electron volts), high strength (~66 gigapascals), and excellent ambient stability. Density functional theory calculations predict a large family of such monolayer structured two-dimensional layered materials, including semiconductors, metals, and magnetic half-metals.

[Clinical features of children with severe adenovirus pneumonia and hemophagocytic syndrome: an analysis of 30 cases].

OBJECTIVE: To study the clinical features of children with severe adenovirus pneumonia (SAP) and hemophagocytic syndrome (HPS). METHODS: A retrospective analysis was performed from the chart review data of 30 children with SAP and HPS who were admitted from January 2014 to June 2019. According to the prognosis, the children were divided into a good prognosis group (n=18) and a poor prognosis group (n=12). RESULTS: Among the 30 children with SAP and HPS, the ratio of male to female was 2:1. The median age of onset was 1 year and 3 months (range 3 months to 5 years), and the mean course of fever was 19±7 d. Of the 30 children, 28 (93%) experienced disease onset in January to June. High-throughput gene detection of serum pathogens showed that 16 (53%) children were positive for human adenovirus type 7 (HAdV-7), and the other 14 (47%) children were positive for HAdV antigen based on immunofluorescence assay for throat swab, with unknown type. Of all 30 children, 29 (97%) had respiratory complications, 24 (80%) had cardiovascular complications, 16 (53%) had gastrointestinal complications, and 9 (30%) had toxic encephalopathy. Eighteen children (60%) improved or recovered and 12 (40%) did not recover (3 died). Compared with the good prognosis group, the poor prognosis group had a significantly longer course from onset to diagnosis of HPS (P<0.05), significantly higher levels of fibrinogen and tumor necrosis factor-α (P<0.05), and a significantly lower level of interferon-γ (P<0.05). The mean follow-up time was 6±2 months; 11 (41%) children recovered, 1 (4%) experienced recurrence of HPS, and 15 (56%) had the sequela of post-infectious bronchiolitis obliterans (PIBO). CONCLUSIONS: HPS may be observed in children with SAP, and PIBO is the most common sequela of SAP.

A FinFET with one atomic layer channel.

Since its invention in the 1960s, one of the most significant evolutions of metal-oxide-semiconductor field effect transistors (MOS-FETs) would be the three dimensionalized version that makes the semiconducting channel vertically wrapped by conformal gate electrodes, also recognized as FinFET. During the past decades, the width of fin (W[Formula: see text]) in FinFETs has shrunk from about 150 nm to a few nanometers. However, W[Formula: see text] seems to have been levelling off in recent years, owing to the limitation of lithography precision. Here, we show that by adapting a template-growth method, different types of mono-layered two-dimensional crystals are isolated in a vertical manner. Based on this, FinFETs with one atomic layer fin are obtained, with on/off ratios reaching [Formula: see text]. Our findings push the FinFET to the sub 1 nm fin-width limit, and may shed light on the next generation nanoelectronics for higher integration and lower power consumption.

A Flexible Carbon Nanotube Sen-Memory Device.

In a modern electronics system, charge-coupled devices and data storage devices are the two most indispensable components. Although there has been rapid and independent progress in their development during the last three decades, a cofunctionality of both sensing and memory at single-unit level is yet premature for flexible electronics. For wearable electronics that work in ultralow power conditions and involve strains, conventional sensing-and-memory systems suffer from low sensitivity and are not able to directly transform sensed information into sufficient memory. Here, a new transformative device is demonstrated, which is called "sen-memory", that exhibits the dual functionality of sensing and memory in a monolithic integrated circuit. The active channel of the device is formed by a carbon nanotube thin film and the floating gate is formed by a controllably oxidized aluminum nanoparticle array for electrical- and optical-programming. The device exhibits a high on-off current ratio of ≈106 , a long-term retention of ≈108 s, and durable flexibility at a bending strain of 0.4%. It is shown that the device senses a photogenerated pattern in seconds at zero bias and memorizes an image for a couple of years.